N‐Carboxyanhydrides (NCAs): Unorthodox and Useful Reagents for Amide Synthesis

N‐Carboxyanhydrides (NCAs) are compounds derived from the addition of a carboxylic acid to an isocyanate, and are known to form amides readily with the release of CO2 as a by‐product. NCAs have been known for over 120 years, but despite their lengthy history, have remained so far overshadowed by more traditional approaches to amide bond formation. In this review, the potential utility of NCAs in the context of amide bond formation is reviewed and their preparation, reactivity and practical application are also discussed. N‐Carboxyanhydrides are species derived from the addition of a carboxylic acid to an isocyanate, and are well‐known to form amides products with release of CO2. Although first reported over 120 years ago, their potential use as reagents for amide bond‐forming reactions is currently underexplored. In this article, the properties, synthesis and current applications of NCAs are highlighted.